Cyclitols such as inositol are found in nature in a large number of plants. Inositol has been identified as a valuable nutrient and was for some time classified as one of the B-vitamins. Inositol was first claimed to have vitamin activity by D. W. Woolley, primarily due to its antialopecia effect in mice. M. J. Jackson, S. Shin, Cold Spring Harbor Conf. Cell Proliferation, 9, 75 (1982). Classification as a vitamin was however confused for some time due to difficulties in analytical techniques for inositol and the successive findings of great variability in endogenous synthesis of inositol in different animals and different tissue types within these animals.
Inositol is not now considered a true vitamin for humans, although it is clear that it is essential for the survival and growth of many human cell types. Animals, including humans, normally synthesize endogenous inositol, but inositol deficiency can exist in animals which can lead to disease conditions. B. J. Holub, Ann. Rev. Nutr., 6, 563 (1986). Recognizing the importance of inositol in animals, especially during periods of rapid growth, the U.S. Food and Drug Administration has set a requirement for inclusion of inositol in infant formulas which do not contain milk (a good source of inositol). 21 C.F.R. .sctn.107.100 (1987).
In yeast, and possibly higher animals, inositol appears to play some essential role in membrane phospholipid balance, and is required for proper growth. See Greenberg et al., Genetics, 100:19-33 (Jan. 1982). The standard commercial source for inositol is corn steep liquor, since inositol is present as phytic acid in corn. See Artz, et al., U.S. Pat. No. 2,615,053, and The Merck Index, compound 4823, page 788, Merck & Co., 11th Ed. (1989).
Traditionally, inositol or cyclitols have been separated from a mixture of alditols and sugars, both simple and complex. Inositol has been purified by selective adsorption on zeolite molecular sieves. Chao, U.S. Pat. No. 4,482,761. Cyclitols can be crystallized from a mixture of sugars, but such crystallizations typically include and occlude a significant number of impurities. Another traditional method of purification is to pass a mixture of sugars, alditols and cyclitols through an appropriate column to separate cyclitols from other sugars before crystallization.